A wheel bearing apparatus, incorporating a wheel speed detecting apparatus, to rotationally support a wheel of a vehicle and to detect the wheel speed is generally known. The wheel bearing apparatus supports a wheel of vehicle relative to a suspension apparatus. It incorporates a wheel speed detecting apparatus to detect a rotation speed of the wheel of the vehicle to control an anti-lock braking system (ABS). Such a bearing apparatus generally includes a sealing apparatus arranged between inner and outer members that rotate relative to each other via rolling elements. A magnetic encoder, with magnetic poles alternately arranged along its circumference, is integrated into the sealing apparatus. Alternatively, wheel speed detecting sensors, to detect the variation in magnetic poles of the magnetic encoder according to the rotation of wheel, can be mounted on a knuckle that forms part of a suspension apparatus of a vehicle after the wheel bearing apparatus has been mounted onto the knuckle.
A known example of a wheel bearing apparatus incorporating a wheel speed detecting apparatus is shown in FIG. 32. The wheel bearing apparatus includes an outer member 50, an inner member 51, and a plurality of balls 52 contained therebetween. The inner member 51 includes a wheel hub 53 and an inner ring 54 press-fit onto the wheel hub 53.
The outer member 50 has an integrally formed body mounting flange 50b on its outer circumference. Double row outer raceway surfaces 50a and 50a are integrally formed on the outer member inner circumference. In addition, a sensor 63 is secured on the knuckle 65 by a screw 66.
The wheel hub 53 includes a wheel mounting flange 55, on its one end, on which a wheel (not shown) is mounted. The wheel hub outer circumference includes an inner raceway surface 53a. A cylindrical portion 53b axially extends from the inner raceway surface 53a. The inner ring 54 includes an inner raceway surface 54a on its outer circumference. The inner ring 54 is axially secured on the cylindrical portion 53b by a caulked portion 53c that is formed by plastically deforming the end of the cylindrical portion 53b. 
A seal ring 56 is inserted into the outer side end of the outer member 50. The lip of the sealing ring 56 slidably contacts the base 55a of the wheel mounting flange 55. An encoder 57 is fit onto the inner side outer circumference of the inner ring 54. The encoder 57 includes an annular supporting ring 58 having a substantially “L” shaped cross-section. An annular encoder body 59 is adhered to a whole side surface of the supporting ring 58. The encoder body 59 provides a rotary encoder to detect the wheel speed. The enclosed body 59 includes N and S poles alternately arranged along its circumference.
The inner side opening of the outer member 50 is closed by a cover 60. This cover 60 is formed of non-magnetic stainless steel plate, aluminum alloy plate or high functional resin etc. and has a simple “flat-U” configuration. It has a disc shaped closing plate portion 61 and a cylindrical fitting portion 62 positioned around the closing plate portion 61.
The side surface of the encoder body 59, forming the encoder 57, is closely opposed to the cover 60. A detecting portion 64, of the sensor 63, is arranged closely to or in contact with the side surface of the cover 60. The detecting portion 64 and the encoder body 59 oppose each other via the cover 60. The presence of the cover 60 prevents entry of water, iron dust, magnetized debris etc into the space between the sensor 63 and the encoder 57. Thus, it prevents breakage of the sensor 63 and the encoder 57 as well as preventing a disturbance or degradation of regular and cyclic variation of the magnetic characteristics of the encoder body 59. Reference Patent Document 1: Japanese Laid-open Patent Publication No. 249138/2000
However, a problem of the prior art wheel bearing apparatus incorporating a wheel speed detecting apparatus is that since the fastening and positioning of the cover 60 relative to the outer member 50 is not reliable and stable, it is believed that the cover 60 will be moved from its predetermined position during mounting of the cover 60, transportation of the bearing itself, assembly onto a vehicle, or after mounting of the wheel due to impact of gravel or the like that would strike it.
In addition, since the cover 60 has a simple “flat-U” configuration, it is believed that the cover 60 would contact the encoder body 59 due to deformation of the cover 60 caused by impact from gravel or the like that would strike it. Furthermore, since the detecting portion of the sensor is arranged opposite to the encoder 57 via the cover 60, it is believed that the air gap between the two would be increased. Thus, the detecting accuracy would be detracted.